Side view of one of Crown Tools 1/4" thick
Shear scrapers. These tools must be used close
to the end of the tool rest for best results
Overview: If you've ever used a one of these tools, you know that you need to keep the edge sharp, present it at the correct angle to the wood and control vibration. No matter how sharp the edge is, if it vibrates during use, you cannot produce a clean and smooth surface.
There are several strategies available to help reduce vibration when using these tools. These include using a tool made from a thicker tool blank, using a tool rest that can be positioned closer to the surface of the wood or by using a specially designed heavy-duty tool.
These 1/4" thick tools are excellent for working
on the outside of bowls, platters and hollow forms
Thin vs. Thick
This Henry Taylor Tools 3/8" thick half round tool is
used for shear scraping inside bowls and shallow platters.
Weight and mass are critical. If you're considering purchasing a new one, buy the thickest tool you can afford. Using thicker tools allows you to extend the length your tool can be extended off the edge of the tool rest and still produce an acceptable surface. Thinner tools need the tool rest support very close to the cutting edge, or they will vibrate excessively.
Side view of Henry Taylor Tools Half Round tool. The thicker mass in this 3/8" thick tool allows a much longer working distance off the end of the tool rest compared to 1/4" thick tools
Normal scrapers made from 1/4" bar stock and work well if the edge of the tool is kept very close to the surface of the wood. That means you need tool rest designs that conform to the profiles of projects you will be turning, so you can minimize any overhang. Since none of us has a custom tool rest for every shape we produce, thicker tools are a better all around choice.
These 3/4" diameter tools were made
from automobile shock absorber rods
Heavy duty scrapers increase the thickness of the bar stock to 3/8" and allow a much longer workable length off the tool rest before the quality of the cut degrades. An even thicker ultra heavy-duty version is available made from 1/2" thick bar stock. Now we're talking!
The large diameter on these homemade tools
virtually eliminates vibration during use
These tools are the thickest you can purchase currently and offer superb, vibration free performance for most turning situations. Of course, everything has its limits and these do as well. At some point, you need tool rest support close to the cutting edge, or the quality of the cut will be compromised.
Close-up view of the bevel grind on my
homemade shock absorber tool
The design of Oneway's straight tool rest allows
it to be positioned inside smaller bowls
Obviously, we need close tool rest support when we're using a scraper. Therein lies the rub… Typical straight tool rests are great for working on the outside of most projects, but are sorely lacking when it comes to supporting the tool for inside work. This is especially true when hollowing deep semi-hemispherical (half-round) bowls, boxes, or tall open vase forms. Unless you have a large supply of tool rests on hand that will provide close support for these types of projects, you have a long road to hoe to control vibration.
The design of "S" curve tool rests allows it
to be positioned much closer to the inside wall
on bowls than a straight tool rest
"S" curve cast iron tool rests offer an option that can be useful for some turning situations; however, the design is limited in its overall usefulness. The width of the tool rest can interfere with proper positioning when working on smaller forms. In addition, the bottom of these types of cast iron rests usually incorporate two mounting holes for the tool post. The area around this secondary mounting hole can interfere with close positioning when working inside curved forms.
Straight tool rests like this Jet Tools 14" long
model offer easy access on the outside of projects,
but limited access on the interior of some projects
In recent years solid round and flat bar stock tool rests that have been shaped into a curve have become available that are much more useful than the cast iron type of curved rests. Round bar tool rests offer more access and clearance for the tool than a cast iron rest and are easier to use for a wider variety of cuts inside projects. The flat bar curved rests are also useful, especially when making delicate shearing cuts.
Extra Long Heavy Duty Tools
Kel McNaughton's shear tool has the correct shear
angle ground into the shaft of the tool. Unlike most
shear scrapers, this tool can be used flat on
the tool rest, producing superb results
When you need to go deep, extra heavy-duty tools from Kel McNaughton are worth their weight in gold. Kel McNaughton's tool features a large 7/8" bar stock, ground with flats so the correct presentation angle of 50 degrees is automatically presented to the wood. The backside of the tool is round, for maximum flexibility in presentation angle. Two versions are available, a short 7" version and an extra long 17" version (not including the tang, or handle length).
The cutter on the end of the tool is adjustable for proper cutting angles and is easily removable/replaceable if necessary. The long and heavy metal handles help to dampen vibrations and allow for good control of the tool when scraping. These tools can be used freehand, or they can be mounted in a captured bar hollowing system like Kelton's Hollowing rig for greater control when working long distances off the tool rest.
Scraping When Deep Hollowing
Dennis Stewart's arm brace hollower can be
fitted with scraping tips as well as cutting tips
Scraping when deep hollowing presents unique challenges since unsupported tool overhang distances can be quite long. One of the ways to help reduce the potential for vibration when deep hollowing is to use a larger boring bar. The larger mass of a heavy-duty boring bar combined with a heavy-duty tool greatly reduce vibration and help to produce clean, smooth surfaces.
Close-up view of Stewart cutters (mounted on boring bars)
and optional teardrop shaped tips (lower center)
If you're into deep hollowing, check with your system manufacturer about getting an extra thick deep boring bar. Most manufactures offer these heavy-duty boring bars as an optional accessory. If your hollowing system manufacturer does not offer one, check another manufacturer. Many accessories are interchangeable with various receiver handles.
Kel McNaughton's heavy duty boring bar measures
19.5" in length and fits into standard 3/4" receivers
on hollowing tools
Safety Note: Always follow all manufacturers safety instructions before working with your lathe, or any of the tools or products you may use. If you are unsure about any operation, obtain competent professional instruction before proceeding. Use and wear all necessary safety devices during turning and observe safe woodturning practices to prevent accident or injury.
Steven D. Russell is a professional studio woodturner, teacher and writer. He has written numerous articles for international woodturning magazines, which have been published in more than 78 countries around the world. Steve has demonstrated in numerous cities across the United States. His studio, Eurowood Werks, specializes in bowls, platters and hollow forms with unique visual and tactile treatments.
Steve is also the current and founding President of the Lone Star Woodturners Association, Inc., an AAW member chapter. The LSWA is a 501(c)3 non-profit educational organization dedicated to teaching and demonstrating the art and craft of woodturning.
Steve is also a featured writer for the Guild of Master Craftsman's "Woodturning" magazine, published in London England. Woodturning magazine is the world's leading magazine for woodturners. Look for his articles covering technical topics, or project based articles in an upcoming issue.